The present invention pertains to a device and method for drilling a secondary or deflection hole from a cased hole in underground rock or geologic formations.
In preparation of a conventional deflection hole or window, a packer is oriented in the drill hole and a diverter wedge unit, including a wedge surface, is mounted on the packer by an anchor device. The deflection wedge unit is usually attached to a pilot window milling tool by a shear bolt linkage and is inserted into the drill hole with the drill string bearing the pilot milling tool. The conventionally employed tool includes a frontal cone oriented towards the deflection wedge unit. The cone forms a deflection guide cooperating with the deflection wedge surface of the deflection wedge unit. After shearing off the bolt joint, the pilot milling tool cuts a window in the tube wall region as the cone is diverted downward.
Once the cone, however, runs past the deflection wedge surface, the pilot milling tool's frontal cutting surface remains located directly above the deflection wedge unit and thus would destroy the deflection wedge unit upon further downward motion. The drill string must then be pulled, equipped with a different cutting tool, and reinserted. Furthermore, any additional cutting work needed to perfect the window, such as milling, widening, and clearing of the same also requires the pulling of the drill string and equipping it with new cutting tools before relowering it. This may take place several times and the attendant work and assembly effort is considerable.